In current semiconductor industry, IC products may be classified into three categories: analog circuits, digital circuits, and digital/analog hybrid circuits. Memory device is an important type of the digital circuits. In recent years, memory device especially the flash memory is developed very fast. The main feature of the flash memory is its nonvolatile property where data may be stored for a long time without a power supply. As a result, the flash memory is widely used in areas where dada needs to be kept during a power off state, and/or where dada needs to be read/written frequently. Besides, the flash memory has the advantages such as high degree of integration, fast reading and writing speed, ease of erasing and rewriting, etc. Thus, the flash memory is often extensively used in microprocessor and electronic systems and automation industries. Thereby, it is important to improve the performance and to reduce the cost of the flash memory.
EPROM Tunnel Oxide (ETOX) NOR flash memory is a high performance flash memory. A cell of the NOR flash memory often includes a floating gate structure on top of a substrate, a source region located on one side of the floating gate structure, and a drain region located on the other side of the floating gate structure. Further, the floating gate structure includes a tunnel oxide layer formed on the top of the substrate, a floating gate layer formed on the surface of the tunnel oxide layer, an insulation layer formed on the surface of the floating gate layer, and a control gate layer formed on the surface of the insulation layer.
As the development of high density flash memory, which is being used as the storage media in portable electronics such as digital cameras, laptops, and tablets, performance of the portable electronics increases significantly. Reducing flash memory's cost by shrinking the feature size of the flash units is a trend in the current flash memory technologies. Currently, for the ETOX NOR flash memory, the conducting structures on the surface of the source and drain regions may be formed by a self-aligned contact process, thus to satisfy the needs of making even smaller sized flash memory.
However, the conducting structures formed on the surface of the source and drain regions through the self-aligned process may still possibly cause the flash memory to have poor performance and low reliability and stability. The disclosed methods are directed to solve one or more problems set forth above and other problems.